1. Field of the Invention
The present invention relates to a ceramic composition for a multilayer printed wiring board. More particularly, it relates to a composition which can be sintered at a low temperature of not higher than 1000.degree. C.
2. Description of the Prior Art
Electronic parts have been proposed wherein circuits and insulating layers are alternatively laminated on a insulating board to form three dimensional circuits. As such electronic parts, there are a first type which can be prepared by printing circuits and insulating layers alternatively on a board such as an alumina board previously formed by sintering, and then sintering the printed board, and a second type which can be prepared by printing circuits on non-sintered ceramic boards, and laminating the printed boards so that the circuits do not contact one another, followed by pressing and sintering.
In the first type, each insulating layer formed on a printed circuit becomes uneven due to the presence of the circuit therebeneath, and the unevenness increases towards upper layers. As the unevenness of the layer increases, it becomes difficult to print the next circuit thereon. This constitutes one of the factors which limit the number of laminated layers. Normally, in the first type, from 5 to 6 layers are regarded to be the maximum number.
Whereas, in the second type, the printing of a circuit is effected always to a substantially flat board, whereby there is no such limitation as in the case of the first type, and it is possible to prepare a product having a great number of laminated layers. Thus, it is possible to attain correspondingly high density integration.
As a material for the board of the second type, a composition comprising from 8 to 16% by weight of alumina powder and glass powder is disclosed in U.S. Pat. Nos. 4,039,338 and 4,153,491.
However, such a conventional composition has an extremely high sintering temperature at a level of from 1500.degree. to 1600.degree. C. Therefore, there have been difficulties such that it is required to use an expensive material such as W or Mo which is durable at such a high sintering temperature, as the material for the circuit, and it is required to conduct the sintering in a reducing atmosphere.